Recovery of nickel and cobalt from laterites by sonic assisted sulfatation

ABSTRACT

There is thus provided a method allowing the recovery of metallic values from laterites by the action of rather diluted sulfuric acid on nickel and cobalt-bearing laterites, at atmospheric pressure and near ambient temperature, assisted by ultrasonic treatment. With an acid concentration in the range for example between about 25 and about 50 weight % of sulfuric acid, under atmospheric pressure, sonication, extracting metallic values from the slurried laterites is thus achieved at room temperature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit, under 35 U.S.C. §119(e), of U.S. provisional application Ser. No. 61/968,029, filed on Mar. 20, 2014. All documents above are incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a method and a system for recovery of nickel and cobalt from laterites. More specifically, the present invention is concerned with a method and a system for recovery of nickel and cobalt from laterites by sonic assisted sulfatation.

BACKGROUND OF THE INVENTION

Laterites can be defined as a variety of sub-soil, much weathered in tropical or subtropical climates, and containing iron oxides, alumina, silicates and, in some instances, small amounts, in percent range, of nickel along with traces of cobalt. Weathering over ages of this type of materials has created a segregation of metallic content, high concentration of iron under the form of limonite being found near the surface, while an intermediate layer, i.e. saprolite, is found located on top of the original bed rock. Nickel and cobalt distribution can vary very significantly between these three levels.

The recovery of nickel and cobalt from laterites is currently practiced in several countries all over the world. The approaches used call upon hydrometallurgy, that is, the use of a liquid leaching medium to collect the desired nickel and cobalt values.

Two hydrometallurgical processes are currently used for the collection of nickel and cobalt from laterites: the Caron method, also referred to as the ammonia leaching method, and the pressure acid leach, also referred to as the PAL method.

The Caron method involves the roasting of the laterites under reducing conditions followed by leaching of Ni/Co with ammonia. This method, typically used in Cuba, Australia and Brazil, is characterized by a very high energy consumption, in particular due to the need of drying of laterite and of reduction, and yields modest recovery, typically 75-85% for nickel and 45-55% for cobalt.

The pressure acid leaching (PAL) method incorporates some variable alternatives but essentially consists in a digestion of the laterite with sulfuric acid in an autoclave at 250° C. under 5 to 10 times the atmospheric pressure. This method is currently planned or used in several countries, such as Brazil, Madagascar, Australia, New Caledonia and Cuba for example. This method leads to higher recoveries of nickel and cobalt than the Caron method, with recovery rates above 90%. But operation of the method can be rendered very difficult or even impossible if the starting ore is rich in magnesium or free silica. Scaling problems in the autoclave result from the presence of these substances that are of frequent occurrence in laterites. Also, the PAL method for Ni/Co extraction from laterites is very capital expensive because of the high cost incurred by material requirements, especially autoclave inert to sulfuric acid at high temperatures.

Therefore, from the current practice worldwide, it appears that sulfuric acid is the desirable reagent for leaching nickel and cobalt from laterite but it is also obvious that the use of this reagent calls for relatively expensive equipment. Equally limitative is the adverse effect of the presence of magnesium and free silica in the laterites, a situation that precludes the use of laterites with high magnesium/silica content but otherwise rich in nickel and cobalt.

Thus, there is still a need in the art for a method and a system for recovery of nickel and cobalt from laterites.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there is provided a method for recovering metallic values from laterites, comprising slurrying the laterites in sulfuric acid; submitting the slurry to sonication; and filtering the slurry.

There is provided a method for recovering nickel and cobalt from laterites, comprising leaching the nickel and cobalt from the laterites with sulfuric acid under sonication.

Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is illustrated in further details by the following non-limiting examples.

A laterite was slurried at the level of 40-50 weight % solid in a sulfuric acid solution 25 weight %, and submitted to sonication, at room temperature and under atmospheric pressure, over a period of 30 minutes. As a result of this sonication, the temperature of the slurry was raised from ambient temperature to about 70° C. After this treatment, the slurry was filtered and an elemental analysis indicated an extraction of 96% of the nickel, 88% of the cobalt, 81% of the iron and 57% of the magnesium, as sulfates of these metals.

Standard procedures known to those of skill in the art, and including for example selective precipitation, separation on ion exchange resins and the like, allow the separation of these dissolved species.

Thus, surprisingly, it was found that metallic values such as nickel, cobalt, iron and magnesium, could be extracted very efficiently from typical laterites with sulfuric acid at near ambient temperature and under atmospheric pressure, using sonication.

In an experiment, a slurry of 100 g of laterite from Cajalbana, Cuba, which composition was, in weight percent: Ni: 0.90%; Co: 0.05%; Fe: 23.9%; Mg: 8.26%, in 200 ml of 25 weight % sulfuric acid was submitted to sonication with stirring. The sonication was achieved with a Hielscher UP4005 equipment operating at 24 kHz with an amplitude of 75%. The power consumption was 174 W, with a sonostrode H22 (titanium, 22 mm wide×100 mm length). The treatment lasted 30 minutes.

The reaction mass was filtered and the analysis of the filtrate showed an extraction of 96% of the nickel, 88% of the cobalt, 81% of the iron and 57% of the magnesium, as sulfates.

In another experiment, a 100 g sample of R.F. (US) laterite was treated as a slurry in 250 ml of 25 weight % sulfuric acid at room temperature for half an hour under sonication as in the experiment described hereinabove. The slurry was then filtered and the analysis indicated an extraction of 95% of the nickel, 87% of the cobalt, 74% of the iron and 72% of the magnesium. The composition of the starting ore was: 1.48% Ni; 0.156% Co, 20.7% Fe and 11.35% Mg, as sulfates.

In still another experiment using a different lateritic material from Dominican Republic having the following composition: 16.1% Mg, 6.1% Fe, 0.88% Ni and 0.011% Co, the same sonication conditions were applied, giving the following extractions: 54% for Mg, 45% for Fe, 96% for Ni and 86% for Co, as sulfates.

In all cases, the initial temperature of the slurry, i. e. room temperature, i.e. about 25° C., was found to have risen to about 70° C. at the end of the treatment, as the result of sonication.

There is thus provided a method allowing the recovery of metallic values from laterites by the action of rather diluted sulfuric acid on nickel and cobalt-bearing laterites, at atmospheric pressure and near ambient temperature, assisted by ultrasonic treatment.

With an acid concentration in the range between about 10 and about 95 weight % of sulfuric acid , for example between about 25 and about 50 weight % of sulfuric acid, for example between about 10 and about 40 weight % of sulfuric acid, under atmospheric pressure, sonication at frequencies in the range between about 10 and about 50 kHz, for example between 20 and 30 kHz, applied for a duration in the range between about 5 and about 60 minutes, extracting metallic values from the slurried laterites is thus achieved, the temperature of the slurry experiencing an increase from about 20° C., i.e. room temperature, to about 70° C. as a result the sonication.

There is thus provided a method for the recovery of nickel and cobalt from laterites, such as limonitic, saprolitic or serpentinic laterites, comprising leaching the nickel and cobalt with sulfuric acid with the assistance of ultrasonic treatment. The laterites can present a magnesium content up to 20%. The sulfuric acid can be diluted to between 10 and 40 weight %. The leaching is conducted at atmospheric pressure and at ambient temperature.

The present method allows leaching of nickel and cobalt from the laterite with sulfuric acid without limitations resulting from high pressure and high temperature requirements, and without restrictions imposed on the selection of the laterites by the need to avoid high magnesium and free silica content as it is presently the case with the PAL method.

The scope of the claims should not be limited by the embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. 

We claim:
 1. A method for recovering metallic values from laterites, comprising: slurrying the laterites in sulfuric acid; submitting the slurry to sonication; and filtering the slurry.
 2. The method of claim 1, comprising slurrying the laterites in a sulfuric acid solution of a concentration in a range between 10 and 95 weight % of sulfuric acid.
 3. The method of claim 1, comprising slurrying the laterites in a sulfuric acid solution of a concentration in a range between 25 and 50 weight % of sulfuric acid.
 4. The method of claim 1, comprising slurrying the laterites in a sulfuric acid solution of a concentration in a range between 10 and 40 weight % of sulfuric acid.
 5. The method of claim 1, conducted at atmospheric pressure near ambient temperature.
 6. The method of claim 1, where said sonication is done at a frequency comprised in a range between 10 and 50 kHz.
 7. The method of claim 1, wherein said sonication is done at a frequency comprised in a range between 20 and 30 kHz.
 8. The method of claim 1, wherein the metallic values comprise at least one of: nickel, cobalt, iron and magnesium.
 9. The method of claim 1, wherein the metallic values comprise nickel and cobalt.
 10. A method for recovering nickel and cobalt from laterites, comprising leaching the nickel and cobalt from the laterites with sulfuric acid under sonication.
 11. The method of claim 10, comprising using sulfuric acid diluted to 10 to 40% in weight.
 12. The method of claim 10, wherein the laterites have a magnesium content up to 20% in weight of said laterite.
 13. The method of claim 10, conducted at atmospheric pressure and room temperature. 